Study On The Efficiency And Mechanism Of O₃/SPC Advanced Oxidation Degradation Of Sulfachloropyridazin

In recent years,the frequent detection of emerging contaminants in the aquatic environment has posed a major challenge to the safety of drinking water quality.Sulfonamide antibiotics（SAs）are a broad-spectrum class of antibacterial drugs widely used in animal husbandry,aquaculture and medicine.Advanced oxidation technology is widely used to remove emerging contaminants.In this study,the O₃/SPC advanced oxidation technology was developed for the degradation and removal of sulfachloropyridazine（SCP）,which had a high detection rate in water,by organic coupling of ozone and an oxidant,sodium percarbonate（SPC,Na₂CO₃·1.5H₂O₂）.The pollution levels and spatial distribution characteristics of the five SAs were first analysed at 12 sampling points in a typical water source in the lower Yellow River area.The correlations between the five SAs and each water quality indicator were then analysed using principal component analysis.The risk assessment of the five SAs was also carried out.The results showed that the total amount of the five SAs at each sampling site ranged from 9.8 to158.85 ng/L.Overall,the concentrations of the five SAs were ranked from highest to lowest in the order sulfamethoxazole>sulfamethazine>SCP>sulfadimoxine>sulfadiazine.The detection rate of the five SAs in the Dawen River water was 100%,with total concentrations above 100 ng/L,a high level of concentration.The total concentration of SAs decreased with flow direction from sampling points S1 to S5.The total amount of the five SAs in the Jiping Dry Canal ranged from 13.9 to 19.1 ng/L,with little variation.The total concentrations of the five SAs in the Yellow River Diversion Reservoir ranged from 9.8 to 30.85 ng/L.SAs had a high correlation with UV₂₅₄,SUVA and trichloromethane formation potential,as well as a correlation with DOC.In addition to sulfadiazine,other SAs in the ecological risk assessment posed some ecological risk at some sampling sites in the study area.The O₃/SPC advanced oxidation technology was then constructed to investigate the degradation efficiency of SCP,including the effect of reaction parameters,common anions and humic acid on SCP degradation.The changes in disinfection byproducts formation potential and mineralisation rate during the degradation of SCP were also investigated.Finally,the application of O₃/SPC in real water bodies was investigated.The results showed that higher ozone dosage and pH contributed to the degradation of SCP.SCP degradation first increased and then decreased as SPC dose increased.Higher SCP concentrations resulted in lower degradation rates.Temperature had no significant effect on the degradation rate of SCP.At a temperature of 25°C,an initial SCP concentration of 1 mg/L,an O₃dosage of 3 mg/L,an SPC dosage of 20 mg/L and pH=7,the degradation of SCP by O₃/SPC could reach 71%.The effect of different anions in the water on the degradation of SCP by the O₃/SPC oxidation system varied,with the three anions affecting the system in descending order:NO₂^->Cl^->SO₄^2-.The degradation of SCP was significantly inhibited by humic acid.The total disinfection byproducts formation potential increased and then decreased during the degradation of SCP.The addition of SPC significantly increased the mineralisation rate of SCP compared to pure O₃.SCP degradation rates were significantly reduced in the actual water column after spiking compared to the pure water spike.The synergistic control of other indicators in the actual water column by the O₃/SPC system was also investigated.The results showed that pH,conductivity and DOC did not change much.UV₂₅₄decreased significantly.The intensity of fluorescent organic matter first increased and then decreased.The active components involved in the degradation of SCP in the O₃/SPC advanced oxidation system were found to be·O₂^-,¹O₂and·OH by performing quenching experiments and electron paramagnetic resonance characterisation.Ten possible intermediates were identified based on Density Functional Theory and results detected by a Waters Xevo G2-XS QTOF high resolution mass spectrometer.Five possible degradation pathways were then deduced,with the main reactions being S-N bond cleavage,hydroxylation,nitroxylation and SO₂removal/Smiles-type rearrangement.The toxicity estimation software tool,Ecological Structure and Activity Relationship,was then used to predict the acute and chronic toxicity of the intermediates formed during SCP degradation.The results showed that the acute and chronic toxicity levels of the 10 intermediate degradation products were either increased or decreased compared to the parent SCP.The combined toxicity of O₃/SPC on SCP degradation products needed to be further investigated.This was followed by a combined acute toxicity test with Vibrio fischeri.The results showed a trend of decreasing and then increasing acute toxicity in the water column as the reaction progressed.